1. Field of the Invention
This invention is concerned with a process for converting synthesis gas, i.e., mixtures of gaseous carbon oxides with hydrogen or hydrogen donors, to hydrocarbon mixtures and oxygenates. In one aspect, this invention is concerned with a process for increasing the yield of hydrocarbons in the gasoline boiling range and aromatic hydrocarbons over that obtained in the prior art Fischer-Tropsch synthesis process. In still another aspect, this invention is concerned with utilizing a novel catalyst composition for rearranging the products obtained in the conversion of synthesis gas.
2. Prior Art
Processes for the conversion of coal and other hydrocarbons such as natural gas to a gaseous mixture consisting essentially of hydrogen and carbon monoxide, or of hydrogen and carbon dioxide, or of hydrogen and carbon monoxide and carbon dioxide, or of hydrogen and carbon monoxide and carbon dioxide, are well known. Although various processes may be employed for the gasification, those of major importance depend either on the partial combustion of the fuel with an oxygen-containing gas or on a combination of these two reactions. An excellent summary of the art of gas manufacture, including synthesis gas, from solid and liquid fuels, is given in Encylcopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 10, pages 353-433, (1966), Interscience Publishers, New York, N.Y., the contents of which are herein incorporated by reference.
It is desirable to effectively and efficiently convert synthesis gas, obtained from coal, natural gas or any other available source to highly valued hydrocarbons such as motor gasoline with relatively high octane number, petrochemical feedstocks, liquefiable petroleum fuel gas, and aromatic hydrocarbons. It is well known that synthesis gas will undergo conversion to form reduction products of carbon monoxide, such as oxygenates and hydrocarbons, at temperatures in the range of about 300.degree. F. to about 850.degree. F. under pressures of from about one to one thousand atmospheres pressure, over a fairly wide selection of catalyst compositions. The Fischer-Tropsch process, for example which has been most extensively studied, produces a range of products including oxygenates, heavy waxy oils, and liquid hydrocarbons which have been used as low octane gasoline. The types of catalysts that have been studied for this and related processes include those based on metals or oxides of iron, cobalt, nickel, ruthenium, thorium, rhodium and osmium.
The wide range of catalysts and catalysts modifications disclosed in the art and an equally wide range of conversion conditions used in the reduction of carbon monoxide by hydrogen contribute some flexibility toward obtaining a variety of different boiling-range products. Nonetheless, in spite of this flexibility, it has not proved possible to produce substantial quantities of liquid hydrocarbons in the gasoline boiling range which contain highly branched paraffins and substantial quantities of aromatic hydrocarbons, both of which are required for high quality gasoline, or to selectively produce aromatic hydrocarbons particularly rich in the benzene to xylenes range. A review of the status of this art is given in "Carbon Monoxide-Hydrogen Reactions", Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 4, pp. 446-488, Interscience Publishers, New York, N.Y., the text of which is incorporated herein by reference.
Recently, it has been discovered that synthesis gas may be converted to oxygenated organic compounds and these then converted to higher hydrocarbons suitable for use in high octane gasoline, by contacting the synthesis gas with a carbon monoxide reduction catalyst and a special class of crystalline zeolite catalyst arranged in a suitable manner in one or more reaction zones. A two-stage conversion operation is described in copending U.S. Pat. application, Ser. No. 387,220, filed on Aug. 9, 1973. Compositions of iron, cobalt or nickel in combination with crystalline zeolites are described in U.S. Pat. No. 3,013,990. Attempts to convert synthesis gas over X-zeolite base exchanged with iron, cobalt and nickel are described in Erdol and Kohle-Erdgas, Petrochemic: Brennstoff -Chemic, Volume 25, No. 4, pp. 187-188, Apr. 1972.